Electrochemical machining method and apparatus

ABSTRACT

An electrochemical machining method and apparatus wherein electrolyte is impinged against a workpiece from non-conductive inert nozzles which do not penetrate the workpiece. The electrolyte is cathodically charged from an electrode remote from the nozzles so that very fine jets of electrolyte may be discharged. The nozzles are preferably made of glass and extend in a group or bunch from a header containing the electrode. The current potential is controlled to effect localized accurate cutting of the anodically charged workpiece by the cathodically charged electrolyte jets from each nozzle preventing overlapping of the cuts as by splashing or random uncontrolled jet flow. The outside dimensions of the nozzles have no effect on the size of the cut. In hole drilling operations, any undesired taper of the hole is removed by increasing the current potential after a through hole is formed to flow the electrolyte in a straight path for removing any stock creating the taper. Since the nozzles need not penetrate the workpiece, they may be stationarily mounted and hole patterns and spacings not obtainable with movable tools are now easily provided.

Andrews 1 Feb. 19, 1974 I ELECTROCHEMICAL MACHINING METHOD AND APPARATUS [75] Inventor: James D. Andrews, Bloomfield Village, Mich.

[73] Assignee: TRW Inc., Cleveland, Ohio [22] Filed: June 9, 1971 [21] Appl. No.: 151,275

[52] US. Cl. 204/129.6, 204/224 M [51] Int. Cl 823p l/00 [58] Field of Search 204/143 M, 129.6

[56] References Cited UNITED STATES PATENTS 3,403,084 9/1968 Andrews et al. 204/143 M 3,409,534 11/1968 Andrews et al. 204/143 M 3,403,085 9/1968 Berger et al 204/143 M 3,440,161 4/1969 Williams 204/143 M 2,937,124 5/1960 Vaughan 204/129.6 2,958,636 11/1960 I-Iershinger 204/129.6

OTHER PUBLICATIONS De Barr et al. Electrochemical Machining 6-28-68, Elsevier Pub. C0,, pages 197-203.

Primary ExaminerF. C. Edmundson Attorney, Agent, or Firm-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT An electrochemical machining method and apparatus wherein electrolyte is impinged against a workpiece from non-conductive inert nozzles which do not penetrate the workpiece. The electrolyte is cathodically charged from an electrode remote from the nozzles so that very fine jets of electrolyte may be discharged. The nozzles are preferably made of glass and extend in a group or bunch from a header containing the electrode. The current potential is controlled to effect 10- calized accurate cutting of the anodically charged workpiece by the cathodically charged electrolyte jets from each nozzle preventing overlapping of the cuts as by splashing or random uncontrolled jet flow. The outside dimensions of the nozzles have no effect on the size of the cut. In hole drilling operations, any undesired taper of the hole is removed by increasing the current potential after a through hole is formed to flow the electrolyte in a straight path for removing any stock creating the taper. Since the nozzles need not penetrate the workpiece, they may be stationarily mounted and hole patterns and spacings not obtainable with movable tools are now easily provided.

9 Claims, 17 Drawing Figures PAIENIE-D EB 3793.170

' SHEET 2 OF 2 INVENTOR. /ames 0. find/ems sywq @WATTORNEYS ELECTROCHEMICAL MACHINING METHOD AND APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to the art of electrochemically forming holes, depressions and grooves in metal workpieces, and more particularly relates to a method and apparatus for electrochemical impingement cavity sinking or drilling with electrolyte jets discharged from non-conductive inert nozzles which do not penetrate the workpiece and having the electrolyte cathodically charged by an electrode displaced from the nozzle tips thereby eliminating bubble formation and making possible the creation of very fine jet streams.

2. Description of the Prior Art Electrochemical machining with hollow dielectric material tools is known for example in my prior US. Pat. No. 3,403,084 granted Sept. 24, 1968. Such prior known methods, however, required penetration of the tool into the workpiece as cavity sinking progressed. In addition, the hollow tools used in such methods had the electrode encased in the tool. The penetration of the tool into the workpiece resulted in the production of cavities of larger diameter than the external dimensions of the discharge end of the tool. Further, the positioning of the electrode in the tool released hydrogen bubbles and created erratic flow patterns of the electrolyte and, of course, required tools of relatively large diameter to house the electrode preventing close spacing of multiple electrolyte jets.

SUMMARY OF THE INVENTION The present invention now eliminates the effect of an external tool dimension on the size of the cavity being formed since the tool does not penetrate the workpiece and eliminates the electrolyte bubble formation and minimum tool size limitation by removing the electrode from the tool.

According to a preferred embodiment of the invention, a plurality of glass tubes with tapered nozzle ends project from a header carrying a single electrode for all of the tubes. Electrolyte is pumped to the header to be cathodically charged by the electrode and the charged electrolyte flows through the unimpeded glass tubes to impinge directly against the workpiece in the form of individual jets sized and spaced in accordance with the internal diameter of the nozzle ends of thetubes and the spacing of these nozzle ends. The tubes can be spaced together as close as desired so that the jet streams will be as close together as desired. Since the tools do not penetrate the workpiece, a stationary fixture can be used for the tools and a plurality of banks of tools can be held from a single fixture to create hole patterns which could not be obtained with movable tools.

The current potential is increased as the cavity in the workpiece increases and when a through hole is formed permitting the electrolyte to flow in a straight path, the current potential may again be increased to remove stock creating any taper effect in the hole for forming a straight bore.

To facilitate drainage of electrolyte away from the workpiece, it is preferred to mount the workpiece ata level above the tip ends of the nozzles.

Acids such as sulfuric acid, hydrochloric acid, nitric acid and citric acid are useful in concentrations compatible with the workpiece. The concentrations will therefore vary with electrolytes having the highest possible conductivity capacity without causing metallurgical damage to the workpiece being preferred. Concentrations of sulfuric acid in the amounts of 22.5% by volume and concentrations of hydrochloric acid in the amounts of 14% by volume are quite generally useful.

Electrolyte temperatures are preferably maintained in the range of about to F. to maintain the electrolyte strength.

Pumping pressure on the electrolyte will vary widely with the inside diameter of the nozzle tools and generally ranges from 10 to 70 pounds per square inch with a range of 40 to 60 pounds per square inch being preferred.

Nozzle lengths may vary appreciably with lengths of from 0.090 to 0.110 inches being useful for very small diameter drilling.

Nozzle inside diameters may also vary with a range of 0.0003 to 0.001 inches being useful for very small hole drilling and, of course, increasing in diameter as desired for larger hole drilling.

The gap distance between the discharge ends of the nozzles and the workpiece may vary from about 0.030 to 0.150 inches in length with an initial gap of 0.070 being preferred for efficient drainage of electrolyte. The gap, of course, will increase as the cavity deepens.

When the holes being drilled penetrate the workpiece, it is preferred to impinge the electrolyte jets against a back-up material which should have a melting point not lower than about 200 F. to prevent electrochemical action on any underlying workpiece areas.

A direct current potential between the cathodic electrolyte and the anodic workpiece is programmed through a range of about 100 to 800 volts D.C. An initial potential below about 100 volts is preferred until dimples are formed in the surface of the workpiece sufficient to direct the jet streams away from the surface of the workpiece. Penetration of from about 0.001 to 0.010 inches is sufficient to form side walls directing the jets away from the surface of the workpiece to prevent overlapping of cavitation or etching of the surface of the workpiece. Gravity drainage enhances the separation of the spent electrolyte jet away from the workpiece. Generally the low initial starting voltage need only have a duration of from 3 to 15 seconds. The voltage is then increased incrementally as the cavities increase in depth. Starting amperages as low as 0.10 to 0.30 amperes may be used until the cavity is sufficiently shaped to direct the jets away from the workpiece, whereupon the voltage is increased to maintain an amperage of around 0.75 to 1.5. The voltage increases may be in increments up to 800 volts DC.

The preferred tool material is a borate glass having excellent dielectric properties and capable of being drawn to form nozzle ends of desired length and interior diameter. The glass tubes themselves may be quite thin and have exterior dimensions accommodating very close spacing. In addition, if desired, the tubes may have flat sides so as to be abutted together in very close relation.

The preferred electrode materials are any conductor capable of resisting the electrolyte. Metals such as titanium, platinum, and nickel are suitable.

The workpiece is usually a metal or metalloid that is very refractory and difficult to drill, although the method and apparatus are also useful on softer materials capable of being anodically charged. Generally the workpieces are hard high alloy steels, nickel, tungsten carbide, tungsten, molybdenum, titanium, vanadium, chromium, and their alloys, although in some cases iron may form the workpiece.

Other and further objects and features of this invention will become apparent to those skilled in this art from the following detailed description and examples including the annexed sheets of drawings which by way of examples only illustrate several embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of the nozzle end of a glass tube directing a jet of electrolyte against the underface of an overlying workpiece at the start of a drilling operation according to this invention;

FIGS. 2 through 6 are views similar to FIG. 1 but illustrating successive steps in the drilling method according to this invention;

FIG. 7 is an enlarged somewhat diagrammatic crosssectional view illustrating a nozzle tube according to this invention equipped with a center post engaging the underface of the workpiece so that the electrolyte jet emerging from the nozzle will be in a hollow cylindrical tube form for cutting a cylindrical hole through the workpiece and leaving a central core;

FIG. 8 is a top plan view along the line VIIlVIII of FIG. 7;

FIG. 9 is a cross-sectional view along the line IX-IX of FIG. 7;

FIG. 10 is a diagrammatic view illustrating a form of apparatus according to this invention;

FIG. 11 is a vertical sectional view illustrating the manner in which a plurality of banks of nozzle tubes simultaneously act on the leading nose end of a hollow air foil workpiece such as a jet engine fan blade held in a fixture according to this invention;

FIG. 12 is a longitudinal cross-sectional view taken generally along the line XIIXII of FIG. 11, with parts in elevation and other parts broken away;

FIG. 13 is a cross-sectional view, with parts broken away and parts in elevation taken generally along the line XIII-XIII of FIG. 11;

FIG. 14 is an enlarged fragmentary sectional view showing details of the tube holder and spacer and also taken generally along the line XIII-XIII of FIG. 11; I

FIG. 15 is a fragmentary side elevational view with parts broken away and parts in vertical cross-section illustrating another tube mounting arrangement;

FIG. 16 is a transverse cross-section of a row of glass tubes with flat abutting sides for close spacing according to this invention; and

FIG. 17 is a-fragmentary view similar to FIG. 11 but illustrating another embodiment where a plurality of rows of tubes project from a single header.

BRIEF DESCRIPTION OF THEPREFERRED EMBODIMENTS In FIGS. 1 through6 a hollow glass nozzle tool 10 according to this invention is illustrated as impinging a jet stream of electrolyte 11 against the underface 12a of a metal workpiece 12 to eventually form a straight bore hole 13 through the workpiece as shown in FIG. 6.

The tool 10 has a generally cylindrical elongated main body portion 10a necked down at 10b to a needlelike nozzle end portion 10c terminating in a tip 10d closely adjacent the underface 12a of the workpiece Electrolyte is pumped through the tubular body 10a, converges at the necked down portion 10b and flows at high speed through the nozzle 100 to emerge at the tip 10d as a sharply defined jet and impinge directly against the underface 12a lying immediately above the tip. The jet stream then flows laterally through a gap 14 between the tip 10d and the underface 12a following the underface as illustrated at 11a until its flow rate is sufficiently spent to permit the liquid to drop off of the underface as shown at 11b.

The workpiece is anodically charged and the electrolyte is cathodically charged in a manner to be more fully hereinafter described.

At the initiation of the hole drilling operation illustrated in FIG. 1, the electric potential between the electrolyte and the workpiece is kept relatively low so that the laterally flowing stream 11a will not tend to etch the underface 12a beyond the area of initial impingement overlying the nozzle tip 10d.

After a few seconds as shown in FIG. 2 a shallow dimple 15 is formed in the underface 12a immediately above the nozzle tip 10d and as soon as this dimple is sufficiently deep to direct the jet stream 11 away from the underface as illustrated at 110 to eliminate the lateral flow illustrated at 11a in FIG. 1, the current potential between the workpiece and the electrolyte is increased to speed up the drilling operation.-

When the dimple deepens to a shallow well or blind hole of a depth as illustrated at 16 in FIG. 3 providing more side wall for directing the jet stream in a more laterally confined flow path as illustrated at 11d, the potential is again increased to compensate for the increase in distance between the tip end 10d and the bottom of the well 16 where the electrolyte impinges against the workpiece.

Then, as illustrated in FIG. 4, when a substantially deep blind hole or well 17 is formed in the workpiece to further increase the distance between the tip end 10d and the bottom of the hole, anotherincrease in potential is made.

Next, as illustrated in FIG. 5, when break-through is accomplished to form a through hole 18 in the workpiece, the jet stream of electrolyte flows through the hole as illustrated at 112 and if desired to protect overlying workpiece surfaces from the emerging jet stream lle, a dielectric back-up material 19 may be provided for the electrolyte to impinge thereagainst. The spent electrolyte is then free to flow over the top of the workpiece as illustrated.

The hole 18 formed as described will have a slight taper due to the return path-of the electrolyte illustrated at 11c and 11d in FIGS. 2 to 4. According to this invention, the straight bore hole 13 of FIG. 6 is readily formed from the tapered hole 18 by again increasing the potential betweenthe electrolyte and workpiece after break-through as illustrated in FIG. 5. Since the through flowing jet stream does not return back through the hole after break-through the increased potential on the electrolytewill cause it to quickly etch out any remaining stock forming a taper within the confines of the stream.

It will be noted that the tip end d of the nozzle remains at the same fixed distance from the bottom face 120 of the workpiece throughout the entire drilling operation and that incremental or constantly increasing potential between the electrolyte and workpiece, as more fully hereinafter explained, accomplishes the progressive cavitation as the surface being worked upon by the jet stream increases in distance from the tip end of the nozzle.

In the event it is desired to form larger holes without electrolytic etching of all of the workpiece metal to be removed, a trepanning operation may be performed according to this invention as illustrated in FIGS. 7 to 9. As there shown, a tubular glass tool has an elongated cylindrical body portion 20a, a necked down portion 20b and a nozzle portion 20c terminating in a nozzle tip end 20d. Electrolyte 21 is pumped through the tube around a glass rod 22 carried centrally in the tube by washers or collars 23 of dielectric material. The rod 22 projects beyond the tip end 20d of the nozzle 20c and is bottomed against the workpiece 24 on the underface 24a thereof covering a circular area thereof.

The emerging electrolyte jet stream 21 is in the form of a hollow cylinder and impinges against the underface 24a of the workpiece around the rod 22 eventually cutting a cylindrical hole 25 through the workpiece and leaving a central core 26 overlying the rod 22. In this procedure, a large hole 25 can be drilled without electrolytic etching of all of the metal out of the hole since the large diameter core of the metal will remain untouched.

As shown in FIG. 8, a circular hole 25 of large diameter is formed through the workpiece 24 and the core 26 is completely free of the workpiece.

As shown in FIG. 9, the washers 23 embrace the rod 22 and the body portion 20a of the tube to hold the rod concentrically in the tube to project through the nozzle 200 in concentric spaced relation from the inner wall of the nozzle to form the cylindrical jet stream 21 of the desired cylindrical shape and thickness. Slots 23a are provided through the washer for free flow of the electrolyte through the tube.

FIG. 10 illustrates suitable apparatus for carrying out the method of this invention. As shown in FIG. 10, a plurality of tools 10 are mounted in side by side relation to simultaneously project individual jet streams against the underface 12a of the workpiece 12. These tools 10 extend from a header 30. Electrolyte from a supply tank 31 is pumped by a suitable pump 32 into one end of the header for flow through the tools 10.

A direct current power source 33 anodically charges the workpiece 12 and cathodically charges an electrode 34 mounted in the center of the header 30 and providing a common electrode for all of the tools 10.

As better shown in FIGS. 11 and 12, the header 30 is composed of dielectric material such as plastic or glass and has a longitudinal bore 35 therethrough closed at a blind end by a plug 36 threaded into the bore and having a fitting 37threaded into the other end thereof coupled to a tee fitting 38, one leg of which communicates with the discharge side of the pump 32 and the other leg of which receives the negative lead line 39 from the power source, the positive lead line 40 from this source being connected to the workpiece 12 as illustrated in FIG. 10.

An electrode wire 41 attached to the negative lead line 39 is carried centrally in the bore 35 by the end plug 36 and fitting 37.,

A slot 42 extends from the bore 35 to an enlarged recess 43 in the end of the header opposite the bored end. The tools 10 extend through the recess 43 into the slot 42 terminating short of the bore 35. Potting compound or any suitable dielectric cement 44 fills the recess 43 surrounding the tool 10 and fixedly uniting the tools to the header to form a straight row or bank in the desired spaced relation.

The tools 10 project a considerable distance from the header 30 and since they may be quite thin and fragile, they are supported and reinforced near their free ends by a clamp block 45 mounted on rigid pins 46 projecting from the header 30 at each end of the row of tools 10. These pins 46 may be threaded or otherwise secured to the header. The pins have collars 47 near their free ends and the clamp block rests on these collars.

As shown in FIG. 13, the clamp block 45 is composed of rigid dielectric material such as plastic or the like and includes a mounting bar section 48 bolted at its ends to workpiece fixtures 49 and spanning the space between the fixtures. Cap screws 50 mount the bar 48 between the workpiece holders 49. The clamp 45 also includes a bar section 51 bolted to the section 48 as by means of cap screws 52. When the bar 51 is tightened against the bar 48, the pins 46 will be gripped so that a rigid assembly 53 is provided for the tools 10 and header 30.

As also shown in FIG. 13, the tools 10 project through a slot 54 provided by the opposed faces of the clamping bars 48 and 51 and as shown in FIG. 14, the slotted portion of the clamping bar 51 is preferably notched as illustrated at 55 forming recesses receiving the tools 10 and cooperating with the bottom wall 56 in the slot of the bar 48 to lock the tools 10 in fixed spaced relation adjacent their free ends.

Alternately, as shown in FIG. 15, the tools 10 can be abutted together if very closely spaced holes are desired in the workpiece and further, if desired, as shown in FIG. 11, the abutting faces of the tools can be flattened to place their nozzle ends even closer together.

As shown in FIG. 17, an assembly 53a of a plurality of rows of tools 10 can be provided with a single header 30a having a wider slot 42a accepting several rows of tools. The potting compound 44 in the recess 43 of the header 30a will mount the double row of tools 10 on the header 30a. The remaining construction is the same as described for the assembly 53.

As shown in FIG. 11, three tool assemblies 53 are mounted between the work supports or holders 49 which as illustrated carry a hollow metal air foil workpiece such as a jet engine nozzle blade 60. The opposed workpiece supports 49 have slots 61 therethrough receiving the ends of the blade 60. Set screws such as 62 threaded in the holders 49 lock the blade 60 fixedly in the slots so that its nose 60a depends downwardly.

The three sets of tool assemblies 53 are mounted on the workpiece supports 49 by the clamp assemblies 45 as described above and the nozzle ends of the tools 10 are positioned to impinge electrolyte jet streams against the nose end 60a of the blade to form three rows of holes 63, 64 and '65 therethrough along the length of the blade. In jet engine operation, air introduced into the hollow interior of the blade 60 will flow through these rows of holes to form an insulating layer protecting the metal of the blade against the high temperature gases flowing over the blade.

The blade 60 extends through the slots 61 in the work holders 49 and since it has open ends the electrolyte entering the hollow interior of the blade can drain freely out of the open ends.

As shown in FIG. 11, the nose configuration and the positioning of the rows of holes 63, 64 and 65 in the air foil 60 is such that the electrolyte flowing through the holes after break-through as for example during the FIGS. and 6 operational steps does not impinge against any interior surface of the workpiece and a back-up material such as 19 is not needed. However, in the event the electrolyte jets through a formed hole to impinge on a workpiece surface which is not to be cavitated, the back-up material 19 would be placed in the path of the jet to prevent the unauthorized cavitation.

The following example illustrates details of electrochemical impingement drilling with fixed tools and workpieces according to this invention.

EXAMPLE 1 A workpiece composed of Hastaloy X alloy in the form of a sheet having a thickness of 0.060 inches was made the anode in apparatus of the type illustrated in FIG. 10. The alloy had the following composition:

0.10% carbon by weight 0.5% manganese by weight 0.5% silicon by weight 22% chromium by weight 1.5% cobalt by weight 9% molybdenum by weight 0.6% tungsten by weight 18.5% iron by weight Balance-nickel An assembly of tools 10 such as the assembly 53 of FIG. 10 had a common electrode such as 34 cathodically charged as illustrated in FIG. 10. The tools 10 had an inside nozzle diameter of 0.031 inches.

Electrolyte composed of a 10% by weight aqueous solution of sulfuric acid was pumped from the supply tank such as 33 of FIG. 10 through the nozzles.

An initial direct current potential of 120 volts was applied for a period of 6 seconds drawing 0.2 amperes. Then the current potential was increased to 220 volts drawing 1.04 amperes. This amperage was maintained by increasing the voltage in two successive steps to 500 and to 550 volts. At break-through of the hole, the voltage was increased to 729 volts to remove the taper from the hole. The amperage was 0.5 amperes during this hole straightening treatment.

The finished hole diameter was 0.060 inches.

. EXAMPLE 2 The steps of Example 1 were repeated with tools having the same inside nozzle diameter and electrolyte having the same sulfuric acid concentration. The workpiece was the same Hastaloy X stock. The programmed power supply was as follows:

Step Voltage Switching 1 60 volts DC. 6 seconds-.18 amperes (timed) 2 100 volts DC. .95 amperes 3 250 volts DC. .95 amperes 4 350 volts DC. .95 amperes 5 500 volts DC. 12 seconds-.4 amperes (timed) The finished hole diameter was 0.0555 inches. The sequence of programmed power supply is controlled asfollows:

Step 1 Low starting voltage-timed.

Step 2 When amperage falls off to pre-set level,

stepping to number 3 is accomplished.

Step 3 Since voltage is higher in this step the amperage will also be higher initially, allowing fall off to be the same amperage setting in Steps 2, 3, 4.

Step 4 Same amperage setting as 2 and 3-higher voltage.

Step 5 This is a timed sizing portion of the cycle. The length of time along with the level of voltage will remove taper.

EXAMPLE 3 A group of twenty tools 10 mounted in the assembly 53 of FIG. 10 were providedwith an internal diameter of 0.010 inches and a nozzle tip end length 0.1 inches. An electrolyte composed of a 15% by weight aqueous solution of sulfuric acid was pumped through the tools and a temperature of F. maintained.

The electrolyte was impinged against a Hastaloy X alloy sheet of 0.040 inches thickness.

A current potential of 700 volts was developed through this sequential steps of Examples 1 and 2. Only 0.8 minutes were required to break through with 0.3 minutes for hole straightening. The following results were obtained showing the accuracy of the hole drilling operation:

Nozzle Number Hole Diameter Hastaloy X alloy sheet material of 0.040 inches thickness was repeatedly drilled by impingement of 10% by weight aqueous sulfuric acid electrolyte in apparatus illustrated in FIG. 10 at different constant voltages with the following results:

.040 HASTALOY x STO'CK Nozzle l. D. Voltage Drill Time (mins.) Hole Diameter The above table illustrates the effect of increased current potential in decreasing the drill time. The time indicated is the elapsed time at the indicated voltage to produce a straight bore hole of the diameter indicated.

EXAMPLE Thicker Hastaloy X alloy sheet material of 0.060 inches thick was drilled by the electrochemical impingement drilling process of this invention using a 15% by weight concentration of aqueous sulfuric acid in the apparatus of FIG. 10 with the following results:

The above tabulation when compared with Example 4 shows the increased drilling time necessary for the thicker workpiece.

In the above examples, the gap between the tip end of the nozzle and the workpiece averaged about 0.070 to 0.150 inches from the workpiece and the pressure of the electrolyte ranged between 40 to 60 pounds per square inch. The electrolyte temperature was maintained below 100 F. and averaged between 82 to 87 F. The nozzle tubes were boron glass. The electrode was tungsten wire.

From the above descriptions, it will therefore be understood that this invention produces very accurate small diameter holes at a very rapid rate through materials which are very hard to drill by impinging fine jet streams of cathodically charged electrolyte against the workpiece from inert nozzles of dielectric material unimpeded by an electrode and without penetrating the nozzle into the workpiece.

1 claim as my invention:

1. The method of electrolytically removing material from a workpiece without penetrating the workpiece with a tool which comprises flowing an electrolyte through a dielectric material nozzle mounted in fixed spaced relation from the surface of a workpiece, impinging a jet of the electrolyte emerging from the nozzle against the workpiece, applying an electrical potential to cathodically charge the electrolyte in an enlarged zone en route to the nozzle and in spaced relation from the nozzle and to simultaneously anodically charge the workpiece, maintaining a fixed gap between the tip end of the nozzle and said surface of the workpiece, controlling the electrical potential and the flow rate of the jet to remove material from the workpiece only at the area of impingement of the jet against the workpiece, and said controlling of the potential including maintaining a low potential until a stream directing dimple is formed in the workpiece, then increasing the potential as the cavity deepens until a hole is formed through the workpiece, and then increasing the potential to straighten the bore of the hole.

2. The method of electrochemically drilling holes through a metallic workpiece which comprises impinging a jet of electrolyte from a dielectric material nozzle against the surface of a workpiece to be drilled, maintaining a fixed gap between the tip end of said nozzle and said surface, cathodically charging the electrolyte upstream from the nozzle in a relatively enlarged zone, anodically charging the workpiece, establishing a low electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period'sufficient to form a dimple in the workpiece which will direct the electrolyte jet away from the workpiece, then increasing the potential sufficiently to continue drilling at the point of impingement of the jet against the bottom of the hole being drilled until a hole is formed through the workpiece, and then again increasing the potential for a period of time sufficient to straighten the hole through the workpiece to a desired diameter.

3. A method of electrochemical drilling which comprises mounting a dielectric material nozzle in fixed spaced relation to the surface of a workpiece, pumping electrolyte through the nozzle to impinge against the workpiece at an area conforming with the inner crosssectional area of the nozzle, creating a direct current electrical potential between the electrolyte and workpiece to cathodically charge the electrolyte in an unconfined area upstream from the nozzle to prevent release of hydrogen at the nozzle area and to simultaneously anodically charge the workpiece, establishing a low, electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period sufficient to form a dimple in the workpiece with side walls directing the electrolyte impinging against the workpiece away from said area conforming with the inner cross sectional area of the nozzle, progressively increasing said potential as cavitation progresses into the workpiece while simultaneously directing electrolyte away from the workpiece after it has impinged against the surface being drilled until a hole is formed through the workpiece, and then further increasing the potential for a period of time sufficient to straighten the hole to a constant diameter.

4. The method of electrochemically drilling holes through a workpiece which comprises impinging a jet of electrolyte from a fixed nozzle against a starting surface of a workpiece to be drilled, maintaining a fixed gap between said nozzle and said starting surface, cathodically charging the electrolyte, anodically charging the workpiece, establishing a low electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period sufficient to form a dimple in the workpiece which will direct the electrolyte away from the workpiece, then increasing the potential as cavitation of the workpiece increases to maintain a potential sufficient to continue drilling at the point of impingement of the jet against the bottom of the cavity until a hole is formed through the workpiece, and then again increasing the potential for a period of time to develop the hole to a desired diameter. a

5. The method of claim 4 wherein the potential increased as cavitation progresses is effected in increments.

6. The method of claim 1 wherein the workpiece is at a level above the nozzle to facilitate drainage of the electrolyte away from the workpiece.

7. The method of claim 2 wherein a plurality of nozzles are provided for simultaneously forming a plurality of cavities in the workpiece and a single electrode charges the electrolyte en route to the plurality of nozzles.

8. The method of claim 7 wherein the nozzles are formed on the ends of glass tubes and the electrode is immediately upstream from said tubes.

9. The method of claim 3 wherein a plurality of nozzle tubes are provided and the electrolyte is cathodically charged immediately adjacent the inlet ends of the tubes. 

2. The method of electrochemically drilling holes through a metallic workpiece which comprises impinging a jet of electrolyte from a dielectric material nozzle against the surface of a workpiece to be drilled, maintaining a fixed gap between the tip end of said nozzle and said surface, cathodically charging the electrolyte upstream from the nozzle in a relatively enlarged zone, anodically charging the workpiece, establishing a low electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period sufficient to form a dimple in the workpiece which will direct the electrolyte jet away from the workpiece, then increasing the potential sufficiently to continue drilling at the point of impingement of the jet against the bottom of the hole being drilled until a hole is formed through the workpiece, and then again increasing the potential for a period of time sufficient to straighten the hole through the workpiece to a desired diameter.
 3. A method of electrochemical drilling which comprises mounting a dielectric material nozzle in fixed spaced relation to the surface of a workpiece, pumping electrolyte through the nozzle to impinge against the workpiece at an area conforming with the inner cross-sectional area of the nozzle, creating a direct current electrical potential between the electrolyte and workpiece to cathodically charge the electrolyte in an unconfined area upstream from the nozzle to prevent release of hydrogen at the nozzle area and to simultaneously anodically charge the workpiece, establishing a low electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period sufficient to form a dimple in the workpiece with side walls directing the electrolyte impinging against the workpiece away from said area conforming with the inner cross sectional area of the nozzle, progressively increasing said potential as cavitation progresses into the workpiece while simultaneously directing electrolyte away from the workpiece after it has impinged against the surface being drilled until a hole is formed through the workpiece, and then further increasing the potential for a period of time sufficient to straighten the hole to a constant diameter.
 4. The method of electrochemically drilling holes through a workpiece which comprises impinging a jet of electrolyte from a fixed nozzle against a starting surface of a workpiece to be drilled, maintaining a fixed gap between said nozzle and said starting surface, cathodically charging the electrolyte, anodically charging the workpiece, establishing a low electrical potential between the cathodically charged electrolyte and the anodically charged workpiece for a time period sufficient to form a dimple in the workpiece which will direct the electrolyte away from the workpiece, then increasing the potential as cavitation of the workpiece increases to maintain a potential sufficient to continue drilling at the point of impingement of the jet against the bottom of the cavity until a hole is formed through the workpiece, and then again increasing the potential for a period of time to develop the hole to a desired diameter.
 5. The method of claim 4 wherein the potential increased as cavitation progresses is effected in increments.
 6. The method of claim 1 wherein the workpiece is at a level above the nozzle to facilitate drainage of the electrolyte away from the workpiece.
 7. The method of claim 2 wherein a plurality of nozzles are provided for simultaneously forming a plurality of cavities in the workpiece and a single electrode charges the electrolyte en route to the plurality of nozzles.
 8. The method of claim 7 wherein the nozzles are formed on the ends of glass tubes and the electrode is immediately upstream from said tubes.
 9. The method of claim 3 wherein a plurality of nozzle tubeS are provided and the electrolyte is cathodically charged immediately adjacent the inlet ends of the tubes. 